10. A positron collides head on with an electron and both are annihilated. Each particle had a kinetic energy of 1.5 MeV. What is the wavelength of the resulting photons? (A) 3.09 × 10⁻¹³ m (B) 6.18 × 10⁻¹³ m (C) 1.24 × 10⁻¹² m (D) 2.48 × 10⁻¹² m (E) 1.24 × 10⁻¹¹ m

5. In general, the resistivity of a conductor increases as the temperature increases. However, the resistivity of a pure semiconductor may decreases as the temperature increases. What is the possible reason of this unusual behavior of semiconductor? (A) The collisions between free electrons and atoms are reduced as the temperature increases. (B) The collisions between free electrons and atoms are enhanced as the temperature increases. (C) The drift velocity of electrons is increased as the temperature increases. (D) The electron density is decreased as the temperature increases. (E) The electron density is increased as the temperature increases.

10. A positron collides head on with an electron and both are annihilated. Each particle had a kinetic energy of 1.5 MeV. What is the wavelength of the resulting photons?
(A) 3.09 × 10⁻¹³ m
(B) 6.18 × 10⁻¹³ m
(C) 1.24 × 10⁻¹² m
(D) 2.48 × 10⁻¹² m
(E) 1.24 × 10⁻¹¹ m

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